The present invention relates generally to semiconductor devices and a method of fabricating the same. More particularly, the present invention relates to a thermal dual gate oxide nodule free SiGe-containing channel device and a method of fabricating the same.
In many instances, dual gate oxide (DGO) devices need to be integrated on the same substrate. As used herein, the term ‘dual gate oxide devices’ relates to devices that are formed on the same substrate, but have different gate oxide thicknesses. For example, thicker gate oxide devices may be formed on the periphery of the substrate so that they can handle higher voltages associated with input/output operations. Thinner gate oxide devices may be formed in areas of the substrate where higher voltages are not present.
A device including a metal gate and a high dielectric constant (high k) gate dielectric increasingly needs materials that may not be compatible with existing methods for forming dual gate oxide devices. For example, such metal gate/high k dielectric devices may need silicon germanium (SiGe) channels to lower the threshold voltage (Vt) associated with a pMOS device.
Conventional processes, such as thermal oxidation, used to form thick gate oxide devices, however, are not compatible with SiGe channels. This is because if thick gate oxide is grown over SiGe, the thermal oxidation step results in Ge diffusing into the regions of the substrate or the gate oxide that should not contain any Ge. In sum, a thermal oxidation step used as part of the conventional dual gate oxide integration process may degrade the profile of the SiGe channel.
Although there is a compatibility problem with thermal oxides and SiGe channels in prior art DGO devices, thermal oxides are of a better quality than deposited oxides. Specifically, thermal oxides provide an improved interface formation between the thermally grown oxide and the semiconductor substrate interface, little or no defects and improved oxide breakdown property as compared to deposited oxides.